Modern printed circuit boards (PCB) used in Server, Desktop and Mobile computers, among others, use surface mount technology (SMT) reflow ovens to solder a large variety of different electronic components to the PCBs. In the SMT process, Solder paste is applied to the PCB, for example, with a Stencil or an ink jet type machine. The solder paste contains chemical fluxes to remove metallic oxides from the surfaces being soldered. The components are then placed on the PCB over the paste using, for example, a pick and place machine (PnP), and the assembly is drawn through the SMT reflow oven on a conveyor. In order to generate uniform, metallurgical and mechanically sound solder joints, SMT ovens use temperature zones to heat the board, the components and the solder paste, in a closely controlled temperature profile.
LGA (Land Grid Array) sockets, like other large sockets, are particularly challenging to solder, because they have many solder joints spread over a relatively large area. It is difficult to heat the large area evenly. The outer solder joints reach proper reflow temperatures more quickly than the inner solder joints. The inner solder joints reach reflow temperature later because of poor thermal transfer through the PCB and the socket. This comes in part because of the large distance between edges where heat can enter between the PCB and the socket to reach the solder balls. In addition, temperature differentials across the LGA socket during the SMT process cause the socket to deform (warp). The deformed socket does not lay flat against the PCB causing uneven and incomplete solder joint formation.
During solder reflow, covers are placed on the sockets to protect the sockets and to provide a surface by which the pick and place machine can grasp and hold the socket. These socket covers may include vents on the top to allow air flow to the socket. The air flow allows the top surface of the socket to be heated which, in turn, heats the connections to the solder balls.